1. Field of the Invention
This invention relates to a method of and a system for laser beam recording in which a laser beam is caused to two-dimensionally scan a photosensitive recording material, and more particularly to an improvement of a method of and a system for laser beam recording in which a laser beam is intensity-modulated in accordance with an analog image signal and is caused to scan a photosensitive recording material capable of recording a half tone image.
2. Description of the Prior Art
In a laser beam recording system in which a laser beam is caused to two-dimensionally scan a photosensitive recording material, it is difficult to record an image having a delicate gradation faithful to an image signal used to modulate the laser beam because the scanning performance of the means for deflecting the laser beam in the main scanning direction, e.g., a galvanometer mirror, is not sufficiently linear, that is, the scanning speed of the laser beam along the recording material in the main scanning direction varies as the angle of scanning direction varies.
When the laser beam moves slowly along the recording material, the corresponding part of the recording material receives a relatively large amount of light per unit area even if the intensity of the laser beam is constant, while when the laser beam rapidly moves along the recording material, the corresponding part of the recording material receives a relatively small amount of light even if the intensity of the laser beam is constant. Thus different recording densities will appear for the same level of the image signal used for intensity-modulating the laser beam. Accordingly, the gradation of the recorded image cannot be produced faithfully to the image signal. This is generally referred to as "density unevenness".
Theoretically, this problem can be solved by controlling the deflecting operation of the galvanometer mirror with a high accuracy so that the scanning speed of the laser beam is made constant over the entire area of the recording material in the main scanning direction. However, this solution would be very difficult and costly to carry out, and would, as a practical matter, be almost impossible.